If present, indicates that the implementation purports to conform
to Common Lisp: The Language, Second Edition.
This feature must not be present in any conforming implementation,
since conformance to that document is not compatible with conformance
to this specification.
The name, however, is reserved by this specification in order to help
programs distinguish implementations which conform to that document
from implementations which conform to this specification.

:ieee-floating-point

If present, indicates that the implementation purports to conform
to the requirements of IEEE Standard for Binary Floating-Point Arithmetic.

:x3j13

If present, indicates that the implementation conforms to some
particular working draft of this specification,
or to some subset of features that approximates a belief about
what this specification might turn out to contain.
A conforming implementation might or might not contain
such a feature.
(This feature is intended primarily as a stopgap in order to
provide implementors something to use prior to the availability
of a draft standard, in order to discourage them from introducing
the :draft-ansi-cl and :ansi-clfeatures prematurely.)

If present, indicates that a second full draft of this specification
has gone to public review, and that the implementationpurports to conform to that specification.
(If additional public review drafts are produced, this keyword
will continue to refer to the second draft, and additional keywords
will be added to identify conformance with such later drafts.
As such, the meaning of this keyword can be relied upon not to
change over time.)
A conforming implementation which has the :ansi-clfeature is only permitted to retain the :draft-ansi-clfeature if the finally approved standard is not incompatible
with the draft standard.

This feature must appear in *features* for any implementation that
has one or more of the features :x3j13, :draft-ansi-cl,
or :ansi-cl. It is intended that it should also appear in
implementations which have the features :cltl1 or :cltl2,
but this specification cannot force such behavior. The intent is
that this feature should identify the language family named "Common Lisp,"
rather than some specific dialect within that family.

It is generally considered wise for an implementation to include
one or more features identifying the specific implementation,
so that conditional expressions can be written which distinguish
idiosyncrasies of one implementation from those of another.
Since features are normally symbols in the keywordpackage
where name collisions might easily result, and since no uniquely defined mechanism
is designated for deciding who has the right to use which symbol for
what reason, a conservative strategy is to prefer names derived from
one's own company or product name, since those names are often trademarked
and are hence less likely to be used unwittingly by another implementation.